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I O AMERICAN SMELTING AND REFINING COMPANY Tucson Arizona

January 19, 1968

TO: J. H. Courtright

FROM: R. B. Cummings

Resume of Tour of Mission Mine

On November 29 and BO I was given a tour of A.S.A.R.C.O.,s Mission unit and the San Xavier North deposit by Dennis Hall the resident geologist.

Mission Geology. Pre-mineral rocks include:

. Paleozoic sediments - the original rocks include limestone, impure limestone and dolomite~ quartzite and argillite.

2. Early Tertiary argillite and conglomerate.

B. Tertiary quartz monzonite ~ porphyry - occurs as a sill - like intrusion.

Post-mineral andesite dikes cut the rocks in the pit and the deposit is covered by approximately 200 feet of alluvium and from 0-25 feet of conglomerate.

Many structural features are present which have controlled ore deposition. The unconformity between the Paleozoic sediments and the Tertiary argillite has been a localizing factor for sulfides. Even the usually unmineralized Paleozoic quartzite will contain ore when it is on this contact. High angle faults and thrust faults have, in some cases~ localized bodies of high grade copper. Through- out the ore zone a set of thin northeast fissures contains abundant sulfides. A northerly trending breccia dike crosses the east end of the pit and contains mineralization of a probable latter stage than the bulk of the mineralization. Pre-ore folding which strikes north- west and post-ore faults striking northeast have further complicated the picture. A large displacement post-ore thrust has probably carried the Mission deposit to its present position from the south. The Twin Buttes deposit may possibly be the "roots" of the Mission ore body.

The complex alteration at Mission can be conveniently divided into two categories. One type involves the feldspathic rocks (quartz monzonite, argillite, and quartzite). Alteration products in these rocks include quartz~ sericite~ orthoclase~ biotite, and clays.

(2)

Quartz monzonite

Argil!ite

Quartzite

Texture is completely obliterated; quartz- sericite in veins and along seams; most of the rock has been flooded and replaced by orthoclase and quartz; some fine-grained biotite; alteration resembles ~speranza more than Silver Bell. Very fine-grained aggregate; probably recrystallized quartz, sericite, feldspar. Mostly quartz; recrystallized

The limey rocks have been recrystallized and replaced by lime silicates. For mapping and identification purposes, three main types ore recognized.

Tactite

Hornfels

Marble

Massive brownish garnet with some epidote; the garnet is known to be of the andradite group. White to greenish; fine grained aggregate of diopside with some calcite; contact between tactite and hornfels may be sharp or gradational; migration of Mg suspected. Probably recrystallized pure limestone; weakest alteration.

The limits of alteration are gradational and known mainly through drilling. The zone is crudely oriented to the north- northwest.

To the north and south it goes under post-mineral volcanics. The zone is two to three miles wide and is characterized throughout by a high sulfide content. The Mission ore body occurs where the chalcopyrite content is high enough to warrant mining.

Hypogene metallization occurs in the form of pyrite, chalcopyrite, and molybdenite~. These minerals, @re present in discrete grains, fractures, and veins.

Ore grade mineralization occurs in all rock types to at least a small degree. Following is a list of the percentage each rock type makes of the total volume of the ore:

Hornfels and Tactite . . . . . . 60% Argillite and Quartzite(minor i . . 35% Quartz Monzonite ......... 5%

Oxidation and enrichment is almost nonexistant. A very thin layer of supergene chalcocite is sometimes present. Depth of oxidation varies from 0-50 feet.

(3)

When the initial figures on the ore body were calculated the grade was .9% copper. In recent years the average grade of the ore mined has been about .7% copper. The molybdenum grade is approximately,.02% MoS2=in the tactite and hornfels and .035~ MoS 2 in the quartz monzonite porphyry.

To the present time about 50 million tons of ore has been mined. The calculated reserves are ll6 million tons.

Operations Ore and waste ~re trucked by 85 ton K.W. Darts and some 65 ton Haulpaks, Forty foot benches are used in rock and 50 foot benches are used in alluvium. The final pit slope is l:l. The stripping rationis 1.5:l in bedrock with a final stripping ratio~< of 3:1. The operating cutoff is .4% coppe~ but this can be reduced to approximately .3 in some of the soft hornfels. Pit mapping is done on seperate milar sheets for each bench. Mapping control utilizes blast holes which have been surveyed and flagged. Exploration drilling is done on 300' foot centers with some inter- spaced drilling.

The mill capacity is 25,000 tons per day. This is between five and six million tons per years. The mill recovery is 93% for copper. Leaching is not use~ as the acid consumption would be quite high.

San Xavier North Deposit The San Xavier North deposit is about Ltwo and one half miles northwest of the Mission Mine. At the time of our visit, stripping had exposed a small area of the leached cQpping on the northwest side of the pit while the rest of the pit was in alluvium. The geology is known mainly through drill holes.

There are two post-ore rocks in the mine area. The Amole arkose is of Cretaceous age. It is intruded by a Laramide quartz monzonite porphyry. The intrusive occurs in the form of a plug with some sills cutting the arkose. The deposit is covered by up to 150 feet of alluvium. Post-ore volcanics outcrop within one mile of the deposit.

The deposit is on the same north-northwest trend which includes Mission. In the deposit it is thought that northeast and east-west trends may be important in ore control. This is assumed from ore trends picked up in drilling.

The arkose is altered to a quartz-clay-sericite rock. Fine- grained anhedral quartz grains are surrounded by a very fine-grained matrix of clay with varying (usually small to nil) amounts of sericite. Quartz monzonite porphyry shows argillic and quartz-sericite alteration with some secondary orthoclase. The clay mineral content decreases with depth indicating that the argillic alteration may be secondary. The alteration zone is probably of the same general width as at Mission. To the northwest, the post-mineral volcanic cover becomes very deep.

A (4)

Hypogene mineralization occurs as pyrite~ chalcopyrite, and some bornite in the form of discrete grains and veins. The pyrite content (chalcopyrite also?) decreasesto the west (?) of the deposit. The quartz monzonite porphyry is not well mineralized and does not make ore.

Supergene mineralization occurs in the form of chalcocite coating and replacing pyrite and chalcopyrite. The secondary blanket varies in thickness from 40 feet on the east side of the deposit to almost 200 feet on the west side. The enriched zone accounts for about i0 million tons of ore.

The east side of the deposit contains an irregular zone of copper silicates,oxides, and carbonates. J. E. Kinnison has suggested that post-enrichment faulting might have elevated the east end of the chalcocite zone into the oxidation zone and a partial destruction of the chalcocite zone would have resulted.

The average grade of the intrusive is .2% copper. The average grade in the arkose is .6% copper with a .4% cutoff or .5% copper with a .3% cutoff. This does not include i0 million tons of leach material at .7% copper and a .2% cutoff. There are 5 million tons of supergene ore in which the chalcopyrite is wholly replaced. This averages 1.0% copper. There is also 5 million tons of partially replaced supergene ore which averageso.7% copper. The primary ore runs .'~8% copper at the .4% cutoff or .44% copper at the .3% cutoff. The ore also averages .002% molybenumwith trace amounts of lead and zinc.

The overall size of the ore body is approximately 1,500 feet with a depth of 800-900 feet. The total reserves are 30 million tons at .~% copper and a .4% cutoff or 69 million tons of .5% copper at a .3% cutoff.

The leached capping is exposed in the west end of the pit and on two small hills to the west and southwest of the present pit. All of the leached capping exposed is in the arkose except for a thin dike in the small hill to the west of the pit. The leached rock contains abundant fine-grained limonite filled cavities. Th~vary in color from a deep dark red to a maroon to a dark maroon. The limonite filling the cavities often have a pulverant, fluffy appearance. These limonite cavities occur as discrete grains and in seams and fractures and represent limonite after chalcocite. They make approximately 2% of the rock.

The "lead" to this deposit was the presence of limonite after chalcocite on the two small hills near the deposit. This fact along with the presence of alteration in both hills (weak in one, and moderate to strong in the other) was enough to warrant a drilling program in the area.

(5)

Operations At the time of our visit, the pit was being stripped by "c~ts~'and scrappers. The final stripping ratio will be B:l for a .4% cutoff or 1.7:l for a .3% cutoff. The exploration drilling was done on a triangular grid with lines 250 feet apart (289 feet centers). The core recovery was greater than 90~. The mill recovery is plus 90%. A leach test was run and the recovery was 80%.

Robert B. Cummings

RBC.ir

&. I

~ Oj~v

A. GEOLOGY

I.

II.

Iii.

OUTLINE FOR A TOUR OF AN

OPERATING PORPHYRY COPPER

IV.

V.

Rock Types I intrusives - types, etc.

pre-ore rocks - types, etc. post-ore rocks -~es i. how close was cover? 2. evidence of basins in post-orerocks

Structure a) major structural trends b) local structural trends

I. had control on ore 2. didn't have control on ore

c) breccia pipes

Al~eration I types - mineralogical, etc.

areal relation to primary mineralization limits of alteration

Mineralization a) metallization

I. hypogene - for all types of host what minerals total sulfide content weight or volume pyrite: chalcopyrite occurrence - discrete grains, veins, etc.

2. supergene - for all hosts what minerals thickness of blanket occurrence

3. oxidation what minerals areal relation of primary mineralization and

alteration depth of oxidation

b) grade - for all hosts I. Copper - average, primary, supergene, non-sulfide 2. Moly 3. Precious Metals

c) size of deposit ~i ~~,$~ I. total tonnage

mined reserve

2. possible extensions

Leached Capping a) general appearance - as indicative of former sulfides b) evidence of age

c)

I

B.

VI. Miscel~neous Guides or Expressio~ a geochemical b old districts inch. placers c topographical - basins? why? d geophysical

regional structural trends

VI. History of Discovery

OPERATIONS

incl. capping studies

II.

III•

I. Mining a) transportation trucks, belt bl slope control c pit ~ ~lo~

final operating

d) waste: ore in ore final - incl. gravel

e) cutoff operating design

fl mapping g exploration drilling spacing: core recovery, etc.

Mill Data a I Capacity b Recovery

Eea6~IDg--grade, capacity, % recovery, fluid loss

HEHORANDUH:TO: FROH:

® ® AHER|CAN SPIELT ING AND REF iN I NG COHPANY Tucson Ar i zone

January 12, %968

SUBJECT:

HISS!ON MINE Br ie f Comments:

k " , -

• , . , o

Hr. J. H, Cour t r ight • C. E. Zinunerman .

General Commentsin GeOlogical. Observations at Hission Hine, S i lver Bell Hine, and Esperanza and S i e r r i t a (Duval Hining Coo)

A v i s i t to the mine area located south of Tucson was/conducted by Hr. R. Limon. Detai ls per ta in ing tO operat ing procedures such as p i t mapping and grade control Were shown in addi t ion to a cornpiete tour of the Mine.

Sumlary o f the I)eposit:

Close to the v i c i n i t y of the deposit the p r i n c i p a l rocks are sediments and small bodies of in t rus ive igneous porphyrles. A l te ra t ion is pervasive and extends a great deal beyond the l imi¢s of pr inc ipa l ,copper concentration approximately 3 by 2 mFleso A | te ra t |on of the fe ldspathic sediments and igneous rock produced s e r i c i t e , c lay, and a l t e ra t i on of limestone fomed garnet and diops.tde. -~

The pr inc ipa l host rock as a group~ the l i m e s i i i c a t e rocks, t ac t i t e and hornfe ls , appears to be then~s t favorable for ore emplacement, The arg---'==--~ltite is less amenable to ore emp|acement. ~ Ore contro ls are to be in ferred, however i do not f u l l y ag reewi th Ki:nnisOn°s remark, ' J . . . c lea r l y did not depend on open channels of c i r cu l a t i ng hydrothermal so lu t i ons ' , t h a t - i s , for the major volume of copper concentrati-on suggesting that unconformable contact between the Papago formation and the underlying s i l i ca ted sediments served as a loca l i z ing fac tor , however an a l te rna t i ve could be of fered: Thrust pre-ore fau l t ing which could have introduced s ign i f i can t amounts of mineralizi i~g f lu ids judging by the fac t that f a i r minera| iza~ion occurs in the otherwiseunfavorable marble. By the general conf igurat ion of the s i l l = l i k e ~ppearance o~ quartz monzonite porphyry int ruding the unconformable contact betweenPaleozoic rocks and the Papago formation, i t appears p laus ib le that th is S i l l would merge into a plug. However, la tera l migrat ion could have readi ly been a channel through a thrust f a u l t forming an interconnected conduit t o t h e NntrusiVe. ( o n i c d i f f u s l o n would probably be essen t ia l l y Cbrrect as the means to produce~the dispersion of gases in the process of i n t r o d u c t i o n o f iron to form iron~|ime s i l i c a t e s along wi th sulphur, copper and minor metals but only a f te r percolat ion upward through a f reer passage or conduit. A major drawback to th is 1~ine bf thought "is (1) the " re la t i ve ly freshness of the gran i te , and (2)~nO minera l iza t ion found in th is fau l t -under ly ing th is th rus t , beli.eved, to be Basement ThrUst. " ' ~,

Conclusions:

The major factor impressed upon the wr i t e r was the d i f f e ren t aspects of leached capping although there is occasional ' t l i ve - i jmonite in the capping, mostly i t is honeycomb a f te r py r i t e . The, r a t i o of size to a l t e ra t i on seems to

k

® • Hr. Cou r t r i gh t , .: =2= 1=12=68

d - - .

be l imi ted to var iables and a f ixed set could be a very prac t ica l way to prospect for other ore bodies. The age of f au l t i ng transvers!ng the mine area could be fur ther looked upon as the means to shed new ) i gh t on th is type of orebody,

SILVER .BELL HINE BriefSunvnary: : . . . .

A tour o f the p i t and general p i t mapping and operating procedures were shown and conducted by the resldent geologists, H. Nuttycomb and R. Edmiston. A b r i e f l o o k e r the capping over the orebody, El T i ro p i t , suggests a much broader and stronger pervasive a l t e ra t i on . Live l imoni te box work was found wide|y dispersed through the zone of a l t e r a t i o n , and by comparison to Hission, bas ica l l y bet ter defined=

. . = .

Summary of ~the Deposi :

There are two operating p i t s : Oxide P i t and the E1 Tiro P i t , The main s t ruc tura l pat tern seems to beNSOEto NSOOE fractures w i th in the ou t l ine o f hydrotherma] a l t e ra t i on . 8etween these two p i t s there is a small unaltered zone=

Minor garnetized limestone is evident at the northern side of the Oxide P i t whereas north and general ly no r theas te r l y t rend there is much sediments at El T i ro P i t , The zone of a l t e ra t i on s t r i kes northwest whereas a f ractured pat tern s t r ikes nor theast ,suggest ing a probable tensionaiJ~attitude between the major s t ructures.

The pr inc ipa l primary sulphide minerals are py r i t e and chalcopyr i te and occur mainly as thin ve in le ts to several inches. They are usual ly accompanied by quartz in sulphide encased by-a seam:of se~ic i te with f a i r l y uniform d i s t r i b u t i o n . The in t rus ive rocks a r e ~ n z o n i t e p andesite porphyry, daci te porphyry.and Aiask i te and post-mineral dikes andesite and rhyo l i t e , pre-mineral dike d i o r i t e , monzonite and hornblende andesite.

Excluding the post=mineral' andeslte dikes, a~| igneous rocks in the northwest trending are hydrothermally a l tered. Kerr analyses show that the known ore bodies are in the more st rongly a l tered area. There are pa r t i a l s i m i l a r i t i e s to Hission= such as the mineral izedl, tact i t .es have been formed by the same processes that a l tered and minera| ized the in t rus ive rocks. Consequently~ i t is hydrotherma) metasomatism rather than contact m~tamorphism caused by the daci te porphyry and the monzonite. Ch to r i t i za t i on and p r o p y l i t i c a | te ra t i on is evident in a l l the pre-ore sequence. (Deuteric in o r i g i n ?)

The deposits consis t of approximately tabular accumulations of chaicoci te from lO0 to 200 m th ick . The major part of the capping over the ore bodies contains less than 0,|% Cu as ¢upr i te interm|Xed with the | tmoni te= jarbs i te product of o×idat iOno Sudden changes in tenor of the ore occur probably by post chalcoci te fau l t s which would t e n d t o blanket or produce reconcentrat ion, and also because of var ia t ion in loca l : rock permeabi l i ty .

Conclusions;.

~There .seems to be no conc|usive-evidence as to whether p o s s i b i l i t i e s fo r a | te ra t i on rules could be laid-down in dvance as a guidel ine as far. ~s vo|ume and grade est imation are concerned a f t e r v i s i t l n g the abovementioned p i t s . However, i t provides a useful precedent, tha t detai led reconnaissance shou]d be done in the area in question, : J

. t

( . ;

Q Mr, Couttright, -3 . . . . . . t~12-68.

Fromacomparison point of view ~etween Mis.sion and Silver Bell from the standpoint of porphyry copper,- i t seems that S|lver Be]| is closer to that ldeall the porphyry intrusives are the major ore carr ier , whereas at Hission the s i l i ca ted sediments are the host rocks. However, t h e r ~ l s no detraction to classi!fY Hi ssion, as a porphyry copper, ~

Alteration is quite pervasive and widespread at Silver Bell , certainly more impressive than at Hisston. Probably scarcity ofoutcrop would be largely responsible for this apparent difference i f we consider rthe magnitude of Mission compared to Si lver Bel l .

ESPERANZA AND, S IERRI~A -~(Duval. Corpora¢ion)~ Br i ef Comments:

, . , q

A tour Of the~Esperanza p i t andLagenera| out]ine of the proposed new p i t for the Sierr ica orcbody was conducted~byres]dent geologist, Mro Bruce Wilhe|m. Indications"that the company is not ready to disclosethe operating Cutoff at which the S ier r i ta open pi t is to be geared is evident, mostprobably 0.3% Cu plus molybdenum values, : ~

The Esperanza and West Espera?za ar~ associated with a broad contact zone that consists of cretaceous volcanic sed lmen~ary rocks and ter t iary igneous intrusives,~Rocktypes range from med|um grained diroi te to quartz monzonite intrdded.mainly, as stocks and s i l l s .

One of the"more favorable host rocks, quartz l a t l t e porphyry 'and quartz '° monzonite porphyry amenable to carry ore, mainly represented as chatcocite, chalcopyrite, pyrite and molybdenite, wasfound in disseminated and as seams and minor slips in fine fractures associated with quartz veinlets. Alteration zone in theqUartz monzonite porphyry ore range to brownish co]Or and have minor grains o f ser ic i te with quartz and occasionallpyriteo Orthoc|ase and plagoc]ase phenocryst has been obliterated by kao)IniZation and ser lc i t i za t ion. Limonite, jarosi te and fa i r hematite a representover the Esperanza. However, very scattered outcrops were seen in the Sierr i ta area, in fact the hYdrothermal a l terat ion appears lacklng within a few feet of the orebody. ~;iMinor development of s i l ica ser ic i te and potash; feidspars were observed on tf fe~ast sid e of the p i t where a minor outcrop obviously in quartz monzonite was~bbservedo.

According to D. W. Lynchms report, "The:Economic Geology of the Esperanza Hine and Vi,cinity," the faults seemt~have exerted an important control on grade and emplacement of the hypogene and sUper9ene ores. These faults carry massive and breccia quartz writh chaicdpyrite, cha]Cocite, pyr i te , galena and molybdenite. This c r i t e r i a couldaiso ho|d f6r the Sierr i ta deposit. With an estimated iO0 mil i ion tons of overburden ¢o be stripped and with the marginal grade avai lable, the tonnage output per day wil l have to be impressive (50,000 T/day).

Gene ral~¢on¢lusions: .... " : " : l J i _

The= b s i c d~lfferences in hydrothermal alterat'ion are as follows:

(a) Composition of[the solutions; -

(b) Compositiono nd- structure of the wall -rock; (c) Temperature and pressureof the.solution.

, L

%r ,. '~

2 - .

! ,

Hr. Courtr i ght:, - 4 , | =12-68

Co.s:equently, the lteratiOn composition scale definitely • chang e from One d i s t r i c t to the ocher. However, !~n the case between • Hisslon, S i lver Bell and Esperanza, t h e b u l k of al l i terat ions.forthe f i r s t two is essen t ia l l y sericiCe quartz; a lso, ch lor i t i za¢ lon:and p r o p y | i t i c a l t e r a t i o n is evident throughout the area. At Esperanza,: Si | i c i f i ca t ' i on appears predominant over "= s e r i c i t e and ~excep¢~for r e c r y s t a t l i ~ a t i o n quartz is no~¢ affected by any type of ai tera t lon . . -

The volume of unaitered rocks:'rel;atlvel!y is greater at Esperanza than at S i lver Bell and jus t about equal to Hission, suggesting (1) e×othermic ef fec t ~ by the intrusives had less markedly influence than.capping (?); (2) f ractur ing is less evident at Esperanza than at=H|ssion and S i lver Bel l ; (3) wall rock chemical reaction and shear Fractur ing-abi l~i ty seems to be indicated at Esperanza where, i .~o , b io t i¢e granodio~ite is-a poor host rock for copper minera l iza t ion; (4) a more complex history"0f intrusion'and extrusion at Esperanza than at the other two propert ies; and (5) fau l t ing , seems to have exerted and contro] led movements and migration of hypogene meta l l i za t |on , and also the main ¢hanne]

: fbr •down percolat ing s o l u t i o n at the Esperanza. = • .

CEZ: trni "2 =

(;ha r les E. Z in, herman

• k

. • ~ % '

; LI

95B

Oetober 5, 1963

0

Mr. Vincent D. Per~y~ Vice President and ~ief Geologis t

The Anaconda Co. 25 Broadway New ~ Yerk~ N. Y.

Dear Vin:

Enclosed is copy of a paper on the Mission Deposit by John Kinnison of our Tucson exploration staff.

Thislmper presumably will appear eventually in the volume on Porphyry Copper Deposits now belng put together by the Geology Department at the University of Arizona.

In view of our discussion at lunch a few days ago during which you mentioned having some difficulty sorting out the rocks in your current d~illing program in the Pima and T~in Buttes' Distrlcts~ I thought this advance copy of Kinnison~s paper might be of use to you.

Yours very truly,

KENYON RIC~RD

a r t . . /

blcc-~Jco~rtright) A/M- JEKinnison ) Tucson

~ t i ~ ~ ~ ~

"A

~ , , f - J

I/ P I I ~ P F I i I t T

%

NO. i 6Z! ~

PROBABLE ORIGIN

Y t

OF MISSION COPPER DEPOSIT

j . G.

FEB 8 977-

John E. Kinnison Geologist

American Smelting & Refining Company Southwestern Exploration Department

Tucson, Arizona

This paper is to be presented at the Annual Meeting of the American Institute of Mining, Metallurgical, and Petroleum Engineers Inc., Dallas, Texas, February 24 to 28, 1963:

Permission is hereby given to 10ublish with appropriate acknowledgments, excerpts or summaries not to exceed one-fourth of the entire text of the paper. Permission to print in more extended form subsequent to publication by the Institute must be obtained from the Secretary of the Society of Mining Engineers of A.I.M.E.

If and when this paper is published by the Institute, it moy embody certain changes made by agreement between the Technical Publications Committee and the author, so that the form in which it appears here is not necessarily that in which it may be published later.

Preprint distribution by coupon only - - see other side for ordering information. J

\

\

These preprints are available only on a coupon basis. The coupon books may be obtained from SME headquarters for $5.00 a book (10 coupons) for members or $10.00 a book for nonmembers. Fach coupon entitles the purchaser to one preprint. Mail completed coupons to PREPRINTS, Society of Mining Engineers, 345 East 47th Street, New York 17, N.Y.

Preprint Availability List is published periodically in MINING ENGINEERING.

EVIDENCE INDICATING THE HYDROTHERMAL ORIGIN OF A "CONTACT METASONATIC" MINERAL SUITED

MISSION COPPER DEPOSIT, ARIZONA

63133

John E. Kinnison Geologist

American Smelting and Refining Company Southwestern Exploration Department

INTRODUCTION

The Mission mine, located in sou~nern Arizona near Tucson, is a recently developed open pit which produces 15,000 tons per day of copper ore. The mine lies on a wide and gently sloping bajada sweeping northeasterly from the Sierrita mountains. It derives its name from the nearby Mission San Xavier del Bac, built circa 1700.

The ore body is everywhere covered by about 200 feet of alluvium, as are the adjacent Pima and palo Verde mines. The geology of the Mission deposit is known principally through the study of diamond drill holes spaced 150 to 300 feet apart. The open pit is in an infant stage and has not yet revealed much of the deposit, although information obtained there by the operating staff, and from a few thousand feet of exploratory underground workings, has added s ignFficantly to the general fund of knowledge.

permission to publish was granted by the American $meiting and Refining Company. I am indebted to Kenyon Richard and J. H. Courtright for criticism of this paper and for their direction during the several years in which I studied the ~iission deposit. Acknowledgment is given to consultant in petrog- raphy, Robert L. DuBois of the University of Arizona.

The only previous publication pertaining directly to the geology of the Mission deposit appeared in 1959 (Richard and Courtright), and may not be everywhere readily available. Cooper (1960) has published a short paper on the district

SUMMARY

In the close vicinity of the Mission ore deposit, the principal rocks are Sediments and small bodies of intrusive igneous porphyries, all of which are pre-ore in age. The bedrock surface is a buried pediment, and only a few small outc?ops protrude from the alluvial plain. These small and isolated knobs, which are the tops of bedrock hills', lie within a large area of perva- sive alteration and constituted one of the principal exploration leads. The very simplified geologic sketch in Figure I shows these features.

Alteration --- the formation of new minerals or textures and the destruc- tion of the original rock character --- is pervasive within the Mission ore deposit, and extends a considerable distanc~ ~eyond the ~ -:~pa, area of c~ooer concentr&tion. The limits of the Rission altered zo~e. although

~ep~hs of ~'!~' in Che Miss~O~ ~° It c ro1~ ou~ ~low the t~st w~s% of the San ~:vie~ ~ne. a~e ~ also p~et~te~ ~ ~II hol~ n~ ~he ~a~y ~ue (8~0 ") ~ S~ Xavi~ Nine (1200' ~o~e o~ iees.) ~i~

-ov~lylng, mine~li~e~- "~ks~ : ~ o .h~re no evi~ence i~ ~resent ~ h wo~L~ indi~.~e i ts ~ , , . ..

g ha~eve%he S l e ~ r t ~ g ~ $ e i s ~ e - C ~ m ~ i ~ , on ghe b ~ i ~ o£

~e~e~ o~c~ o~ ~ ~ . ~%e name Sger~i.5~ ~ n i ~ e ~ s ~PBL%e~ to

,~1%~ c~ms~euous ~i~ ~ ,~m~s Of ~ovIZe-l~io%i~e~ ~s~ c~nl~ sltere~ ~o chlorl%e. The~%~ps ~na ~ ~ie In%e~eg~s of ~%e b e ~ %he

~ r e ~ b u ~ t ckle~i~e~ ~na ~%so % h e . , ~ ~ .in %he Twin B~%%es e, rea . .~ teh

is o t h e ~ e .......... ' " " .... " ~ ~ I ~ ~ ~ . ~n ~.,¢~0~ hill ~s ~les He!me~ I~.~ ~ e ~..e.rl~s ~ sed~.men%~ry contact ~tith

~ s o ~ % ~ vlth, .C~mbrA~n ~IS~,~~%~ ~. The: ~on$s'cgs ~re ~re~minez~l i~ul~s. Contacts .vi%h p~st-~am~i~n fo~t~ ~ ~ - ~ l ~ y s faults in those ~l~s ~e~-e X hs~e .seen %hem,_

, ' ./

, 4 - . . •

. . •

Heime~ P e ~ ~ o l o ~

. • . .

- . k

~ 7

: i @

J

3.. ( t ) ' • - O~ Xeuolith~ ~ a~ ~c~on occ~n~ ~n ~he Sie~ ~ ~ ~ea~ ~n~ F~II~ T~iu, Buttes,

l~e eAor~ "~he base~sn~Bo~s e~t. ~ cc~c~ appeara ~ be seli~en- ~a~yln the l i t t le ~ I I s O u t h ~ o~ H ~ Pe~. D ~ o r i t e b o ~ e s a r e com- mon to. the ~nl te~ an@ ~ InEi~eet e ~ e ~ i ~ r to be ~ m g e ~ ~ u the

%o "be ~nt~m~ve into ~h~eoz~ic ~ e ~ . ~ e ~ - e Of t ~ ~l~t~al ass.oci~tlon

- - - - - - ~ - ~ - - - - - ~ - - ~ ~ " ' " ~ . . . . - ~ • ~ ' " ~ t e r ~ e t ~ t ~ o f ~t~ctu~e i n the ~n ~atte~ ~zea in ~h~'Oh the ~e~l eore of ~em~te is ~Ufe~r tO be ~-- . Gamb~.. • '

" . : ? .

, . •

C ¸ . '~ r .

• r .

]

. . .,-

~ .

- o

- " , "k

. ! .

,ll i ,

I J

4 " / /

• - I.,¢'o~,'~I-

... " \ / / 1 _ ~ / .--.

/ 1 ..., -"

\ r

MISSION t

ORE BODY '

PIMA PIT ' T t6 S

T I T S

( ~ R E D H I L L m~m el: It) - - [ -

n - . ~ . r

i

EMMONS RANCH

A l l u v i u m E

. . . . . . . i.

F-- -¢b

" ,i NOTE N(~ s t r u c t u r e o t h e r than Base [nen t T h r u s t a n d f a u l t s c u t t i n g S i e r r i t a g ran i te is s h o w n . , • -

. . . . . . . . . . . . . . . . . . . . . . . . . . . . :5 - - ! - ~ . . . . . . . ~-- . . . . -~ --~ " - . . . . . . . ~ "

\ \ ~ ~ ¢ V I L L A G E

7"- ~"~ ," / \ " , / ' / . k , ~ MINNIE "~ =

. . . . . . . . . . I- . . . . . . . . . . . . . . . . ~ - ' ~ . . . . - ~ - - - t ' - - ~ - - - ' - - t f . ' F t ~ . . . . . . . . . . . . . . .

~" s . ...., ~-'-~.-:..--:,,,_ /

i 4 , 4;b - ! / / - - / \ - - P ! / 4 _ \ -

' ¢ ~- ~~b--'~" ~ , \ . ~ b ~ ' . . I 4: :

. . . . . . . . . . . . . . . . . . . . . . J. ~ _ . _ _ $ ~ _ _ _ . . . . . . . . . . . . . . . . . . . . . _ _ j _ _ .

T e r t i a r y "F ~ , ~ P I M A

I

®

EXPLANATION

i

i

IGNEOUS

i ~ t ~ k p r e - C a m b r l a n S i e r r i t a c J ran i t e

~ Tertiary granite

S E D I M E N T A R Y

C a m b r i a n B o l s o q u o r t z i t e

P o l e o z o i c to

T e r t i a r y

MINING DISTRICT

Sketch of outcrop distribution

of SIERRITA GRANITE

SCALE I"=imi,

. I I - ~ ~ Paleozoic IS.

area .~o \ ~ " I "~ ~.~ \ \ \ Pre-mineral fault Cretaceous (?) ~ ~. \ \ \ ~ localizes Minnie--

clnstic sediments / / / " ~ ~.. \ " \ \ Glance deposits. Talus (slightly meta.) 7 / / I' ql"z vein, \ '1 \ L

~ash ~ ' ~ - ~ / -~- o . . . . was. ~\~....~'~ 1 ~ " / / Talus sheared granite \ t ~ / '

~'~,~ ~2~ I / /~ ~ Sierrita granite -C ~" A h ~'AI " i " ~ " / / . >Sierr l la - / ~ ."~1 "' L ~ / < ._~q.ronite . . . . ~"~ (gnelsslu)

Balsa q tz i t e / Pro}. ct.

(overturned near granite} ?

, Length of Section, 4 0 0 0 '4-

DIAGRAMATIC C R O S S SECTION Looking West

M O R G A N - M I N N I E M I N E A R E A

@ ® t

t G~OL.O!}Y OF '~iE {,!~ISS!ON COPPEP, D:~IPOSiT. ,;GI:::ONA

'~"-. °~'~~. O'R r~r"e "bOdy. ~ d I.'~ ....... ~' % O~¢...b. :~.~ .............. . ................ ': ~m

O.f '~;-:he GPe b~:@v

suit.ants R. L,, :>£oois ('pet'.~o~;r:~hy) a:nd Do L. Bry:~nt {~%~'~oti.- Cr:~:,:hy).

f~ D.i~overy o? PIA4 klne by United {}~oph

|

<):

f ~

I

. . . . . . J i l i ~ ll~" , ~ i ± 2 . < +' ..... l l t e 1 . n d . x ma~

P o s i t i o n - o f Mlealon and or.her mines, - ....

' A c r o s s - s e c t i o n e x t e ~ d i N sou th f~Om B l ~ k M o u n ~ l n (pe ,: .... to ~ap) shows the ~oes s t r u o t u r a l F e a t u r e s . :, ~,

• his e oss- ot on mo , Seo t lew-w e /'mlt

~ l s ~ o n d r i l l h o l e s . Po in t ~ ~ ~ , - '

! D~eouse ~ or t m ~ l t - - ~ o f l y . ' ~,'~:~

I Iq in t lo~ t l ~ e x t e n s i v e ~ w e l l d e v e l o p e d pedl l lmrt t ~ ~ n o ~ fl-om Miss ion i r e s . Po ln t t o p r t n ~ l p L l r eek u n i t s . •

e

,# A v ~ y s i m p l i f i e d dle#~Pm, ~ e ~ t l o ~ l se~ le o x a l l ~ t ~ , . Nle41on a l t e r e d zor~. ,,

Po ln t to e l i d e , sho~ln~ ex~eni o f p e r v u t v e ~ k I ~ e F B t ~ p o i n t out l i m e - e J l l e a t e zone, J l rd ; l on lnt~Puslves tltS~ a l ~ P am s] Ido.

s t maJo~ ~ , :me lus l o~ - t o be e m p l t F t ~ a i e ~ o f 1 ~

s p e o l f l e s p a t l a l r e l a t i o n s h i p t o old, her ore ~ alt~eINML~.

2. a l t e r i t J o n and mallph:Lde 1J~Pei~nat lon ~ me o o n t ~ m q ~ ' e n e o u s , Alterat; :Lon. a s ~ h e r ~ p l ~ l ~ k h e t i ~ or' lm , p l u z i e s ~ lt.my hos t ~>oke. _ ' Ib i s i s no t • m t ~ l ~ a a o - ~ l l e ~ o o n t u t m e g ~ a l ; l ~ " e t T e e t .

• ~ 3 . ~ T ~ e t ~ n w u a lzeoeees ore m ~ o e 1 ~ tm i l ~ ~ l ~ m m ~ o f sullmSetes. Na~m e m m e l l o t 0 N n a ~ i..~ ~elee v t d e ] 7 spies , d , %

t~.. Ti~e M1881on lnlrm :111 s " p o r p h y r y ooppe r" d41epomJL~, .

P o d O • wmvk.l.r~ put,posses ~ etesl~14P'aOb$o tat,l, t l udL~htn, b ~ g l v e n speoiL1 names.

- P o l n t ~ t o n i p , l i ssome 1Pwa~o, IPJ3~ m d itZem f tRMi-~ ~ a n d p robab le ~ . Ren~ldm I i ~ ' o f Palp~Bo ~ i N < " se t , r e l a t i o n to Pl~a n t ~ h m ~ l ~ w a l l .

' Point out ore ~ I s t r l bu t l on pattern, and ~aJor ore-ore faults. Ore-ro~k tyoe~: a r g i l l i t e c~orlse~ ~5%, altered lime- etomes of Pim~ formation c~mprise 7~%. Grade of the ore body is comparable to that of other open ~It porph~'~ co;~er ~lnee in the ~o~thwest. Range of grade i~ from .O5 up to i~ ~u.

R1ra~al I zat ion Ida ~ ~

i m d l P a l o Verde m i n e s . A l l r ~ c k s w l t h ~ n t h i s s ~ e a m-e a l t e r e d and im~e~at~.~ with s u l p h l d e s .

! Ola~tlc. eedlmmnts and i~neous - quar tz -se r l c l te or qu~rtz- c~taoc i ase a l t e ra t i on .

' L~m~ sediments -gomnetS, dlopslde, and other Ca-elllcstes.

O~tsl~e th l~ zone the rocks are unaltered and contain no aul[~hlde s.

Discuss cco~poslt~on of hornfels ~nd tactite. Diopslde-

~ d~.berllte. Alberatlon to actlr~l~te. Composition of g arnJt aaa a i e ).

• , ~ulon ore deposit differs from the altered zone only in the i ~ l a t t v e ~ a n c e o f (~u and i t s a v a l l a ~ i l l t y t o ~ow c o s t @pMl.l&lt mlr~ing. Sulphide mlnera ls L~e pT.~,ne~os/ly Fy ar~.Opy.

~ t n o l b o r n t t e . Some s h a l e r t t e and gaAeha.

nAtlo Of I~J/C~M in the ore body varies - elaborate bl-lefly.. T o t / l s u l p h i d e eon~ent--bet~een .5-I0~ g e n m r a l l y .

~ba lcoc l~ Is c ~ I n ~ 1 t o t h l n : . b l a n ~ t . Ox lda~ l~ is 1 0 - 3 0 t ~ _ _ O h a l e o o l t o l a d oxide o¢~ makes ~ u , a f r . t l o r ~ o f o r e m e _ s e t q m _

e

. The a t ruo tu re o f P i s s f o r m a t i o n ee~imenes :Le ccmrplex in p a r e s of ~ e body. Dmt l l~a t sre fo ld~ s~d ~ th~uet / 'sul~s~

S l ide 4 - ~;ectlon throuEh e a s ~ pa~t .

Polnt out t h r u s t f a u l t s , bedding a t t i t u d e s , gene~al d i s t r i - bu t i on of copper.

(Bl lmd notes ?his l s 1500 W s e c t i o n , which w u shown i n the d e d i ~ r t l o n f i l m by Western gnapp. Assa~ra $r$ not l e g l b l e #hen pro jec ted i n t h l e manra~ I~©muso o f the m a l l s ize o f l e t t e r i n g . )

;t.r'a~Tura~ feat~re:~ contrc,~2 t~,~2fLde ~e~ioslt.lon .

• A. ~a4t vein B . Oneonfo~mlty • O. Quar tz l t 4 b e d s .

MortJnea~t trending ~raotures awe oommordy mineralized but sho~ no relation to surrounding disseminated sui-

; phldes.

oone ~ualone 8

~r~se~as t ~ Smme~r~, o f ~ i ~ r u m £ o ~ . ~ d r e l a t l o n s ~ l p , ~ y r y r ~ t~ e l a e ~ o~ l t - - ~ o zone e4' m e a ~ r e t l o n . N~t~ ~ a t

Is l t ~ e l f alnersil~4~J ar~ ea~es t~pleal "protoee e

I Note that sulfides ~re consistently dls~eminated in altered

zone~ and that no al~eratlon Is without sul~hldes and vle~aee~ea. ?he oommluslon As t4~at ~heee two features - sulphldes and alter- atlo~ represent e~ne~r~ent events.

"~O~ee~s8 t~e wide spaelng beL~een la~wn majo r eharmels which looekllse~ h~l~4~r trade eo~eontratAem, and ~he role of' dlfi~ee~ i n emplaeement o£ su lphtdes, and alteration.

Diseuss and elaborate on ~he aspects o£ al~eratlon and wade dlsmln&tlon ot sulphldes, eonelu~11ng that the Rlss~on deposit l e a p o r p h y r y coppe r 4 e ~ o s l t .

~eaelse~ to o¢~r ~poelts, Of ~he ~~e7 eeeper ~pea- 1be ~eaet~bed In &he l i t e r a t u r e , the Wisston s i t . zone most e l o e e ~ y ~ o u ~ b l e s ~ e ~ l y p o ~ r y e ~ p e r b e l t , b o o , u s e a t E ly m o ~ ~e~ts 11e ~ll~hln t h e a l t e r e d zone t h a ~ a t ~oe~ oth~ne • P m S h F ~ ~ t l s t r t e t e . A m o s t e x o e l l e n t deeeePlp~iom ot ~ dAs~a*l~

~ In 0 .8 .0 ,S . P~of. Peter ~J~, A. C. Spen~er. 1917. ~he ~ i ~ e ~ e a e e s a r e e t 4 e l ~ e e on ly ; a~ lrA~ ~4~ere ~ e l ~ mc~ ore In p~e~ ml ~eee In altwee~ eedi~e~m ~,m ~ Rieele..

~be feilO~l~ q ~ : e s present ~pe~cerOe views on the hlstor~f o~r ore 4epeei~t~ at ~ly~

A ,TWo k!~e+ot llt~m~i~ of t4~e rooks of the dis~ie~ are+ e~e~4La~shed. ~ r ilpmemJ metam~am are inc lude4 all those ILl~e~atAo~e MlliOh grttol~led or follo~ the invasion of the eedi- mrnt~ formatlons by the n~atie Rterllkl that eventually e~stalllzed am mon~nl~e lm~phy~. ~ese alteratlons have affected t4~e invaded ll~omms and ~ale8 and also the Igneous r~eMa ~ m s e l v e s . To t h i s n o ~ : e m o ~ l m a as t o b e a t t r i b u t e d t h e f o r m a t i o n o f t h e P r i m a r y me4~a l l l f e r c~s d e l ~ S l t s o~ t h e d l s t r t e t . "

® O

~,,~ ~_.., I....~.:.,~..~. o~. porphSr'f:]! ~ ~.'~'t~'~'.~s ' ~'- hag °~, etW'~h ~.f

¢~ . . . . . t~t~.,, ,~, 3Zw% " r % o w

~,~ ~ Z~ ~ ~.. ~ . . . . . . . . .

t,t~e .,,ot,~:~a! f a o l e s w'h.tca~ ~ r e e ~ . h l b i t ; e d ~.r~ , s , , , . , . . ~ . , , ; ~ . . o~ , , ..... 4 . . . . . . . . . . . . . . . . . . ....~

w i %Y' * ~ "

~@°~e ~"~O~v'~'}~5'~ ~' ~ ~ " ~ * ~ t ~ , @ ~ i : ~

t

. "The depo~l~.!~r <~' :,,,-r~ ~ :~,: : ;~ ~ ,jrJ.te !r, :IA~er~Lr:~ted

old,. :Imes~or~, ~",d ~,,~:c whe:, ,~::'ovdly con~i,Jered, w~s merely an incident of the '~e~'v c~plet~e ~er~orn~i~ of ~,he~e bodl@s of roc~"

"The escape of these solutlons oec~red after tee now meta- morphosed bodie~ of porphyry ~,ad oonso~[Ida~)d, bu~, It I~ oon- eelve,1, at a time net long subsecr~ent to th~s consolidation. =

• "~itroughout the central zone of .the ~ly d'istrlet ~he effeots o~..iwa~..ous me tmmor~Ima are seen in the i n t e n s e and thoroughgoing aAv~a.~on or very zar l~ masses eL' porphyry, l lm~stoa8, and shale. ~ o ~ r~e diFFerent . ~ k e have yielded to c~a~Ical r e o r g a n l s a t l o n am~ ]~e ms~ascma~le r e ~ i a e e m e n t , each in a manner dependln~ p r l -

. ~trIA. y o~.. 1re. o r i g i n a l eompostt loa, yet the ~esu~tlng products are aXA ~eavz~y c~a~ge~ with p~l~e, and In t tm main this m i n e r a l Is acce~anled by minor m~ts of ahaleeq~y~ite. In a ~neral way

t ~al~Ides are e~enly dlstrl~ed th~oug~ the altered r~eks,

10

~e teno~ o~ then ~ An~$eates s~enee~'s ~el~, based em a lem~ and careful S t ~ 1~ha~ ~ t ~ r a t l c m aa~ s ~ A ~ s are , In a,~ea~ s e n s e , c o r s e l e t S , sad t h a t the t a o t l t e | and o t~er • ~te~ ~lmen~e mash e lameseally ~ be ter-~d eoatNt meta- l,s, are ~ be ~1~m'44~ as an Aates~a~ part, o t the porphy ry

'eoppo~ zor~ o f ~ l t o r a ~ l o n .

-s~Iiea~e minerals, ~ elassleal "cor~ta~t ty~e~ ece~ along ~le L14~ehbu~K ~ l t , wel l aw~r A'ro8 a, ~ o e m igneous mass.

lie s t a t e . , i ~ be r~.~d in t1~m. ~h~r~; ~ s ~ m r Or the alteratlon ste~es cam " is no direst ev~~ to Ir~leate elt~e~

eem~mity of de~eitlo~ or a time b~ea~ An the dep~AtloneS , . m , t

• o~J~ted, .WaS .(~f ~ s~noP~'dM~atAon am t,o~e l n a l g r ~ t f l c a n t , " m • ~ e

.~ . Th a l t e r a t i o n , t ~ e ~ f o r e , As o o n s l d ~ as a eonl;Anulr~

~ ~ ~nelr ememlcaA proper~lea, m, .e more In~Xmemee~ by the nme~e oo lme~r env~rorment of dieposlttem than by ~ ~ss eha~ in eem° V~et t ton .

Zonln~ halos of alteratA~n and au!p.~e are attributed to ~atlnulng growth of each alteration halo, away from feeder-velns, ~ t~ the Ine~r halos, exp,~ai~n~ and t~piaclr~ the halo e~meent.

eerme:~e clay envelc~e at ~e. ~l~leT's earef~d work l~lestes mm~ther l~-silleate ( m o e m t ) ] ~ I n ~ l o h , Qe~t ra ry ~ c e s R o n . ~mt1~ oi" early ailleatlee f~lem~d by rraeturin~ and sulphide:: ~ 1 ~ , the s111e~lon a~ J, al~Ide fermatlon axe e e l -

# e